Editor's Note

Magnetic semiconductors are materials with good band conductivity as well as magnetic order. Since each phenomenon requires a different description of the relevant electron states, the band structure of these materials is very complicated, containing band states as well as localized states. An important condition for strong interaction between the magnetic and the conducting electrons appears to b...
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Superexchange mechanisms, which are mostly responsible for the nnn exchange constant I2 in Eu chalcogenides, are investigated in detail. In contrast with the usual 3d transition metal compounds, the Kramers-Anderson mechanism is estimated to be one order of magnitude too small to explain the experimental results due to a small 4f → 2p transfer energy. The mechanism by which a p e...
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UP, US, and the UP-US solid solutions have the NaCl-type structure and are good conductors of electricity. UP is anti-ferromagnetic of type I; US is ferromagnetic. Assuming U4+ cations, P3− and S2− anions, and RKKY interactions between the uranium localized 5f-electrons via the conduction electrons (≈1 in UP and ≈2 in US), the observed m...
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The transition metal dichalcogenides exhibit a wide variety of both electrical and magnetic properties, from insulators to superconductors and from ferromagnetism through antiferromagnetism to diamagnetism. NiS2 is a semiconductor with an anomalous paramagnetic behavior which leaves in doubt the existence of a local moment. Previous neutron diffraction data have failed to show any order...
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The low-temperature specific heat of a series of semiconductor alloys of the SnTe-MnTe system, for Mn to Sn ratios of 0 to 0.1 has been measured in the temperature range 2 to 25°K. Large anomalies are observed due, presumably, to the ordering of the Mn++ spin system. The temperature region over which these anomalies occur is roughly the region in which ferromagnetism is observed.
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Hall effect measurements were made on a single crystal of magnetite in the temperature range 65 to 373°K. The Hall voltage was positive over the whole temperature range. The results can be explained by assuming that magnetite is a normal semiconductor below the transition point and a degenerate one above that temperature.
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The mechanism of electrical conduction in the magnetic semiconductors NixFe3−xO4 with 0.6 < x ≤ 1 was investigated. The electrical properties of these compounds are extremely sensitive to the presence of α-Fe2O3 as a second phase. The exponential temperature dependence of the electrical resistivity ρ and the tem...
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The metal-insulator transition in the V2O3 system is discussed. A recent series of experiments on V2O3 and (V1−xCrx)2O3 is reviewed. The phase diagram for the system is described. The Cr-doped mixed oxides are insulating at room temperature for x ≥ 0.009 and transform to a metal with the applicati...
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Samples of polycrystalline (La1−xCax)MnO3, where x takes values ranging from 0.005 to 0.3, have been studied experimentally. Specimens were carefully prepared in the stoichiometric forms by changing the oxygen partial pressure conditions for each value of x. For specimens having x smaller than 0.1, the Néel temperature TN is almost constant...
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The band structure of materials in which both localized and itinerant outer electrons are simultaneously present is discussed. The Franck-Condon Principle is applied, and small and large polar on formation is taken into account. A scheme for estimating the densities-of-states of perfect crystals and doped or non-stoichiometric crystals is suggested, based on the ionic many-body states as a startin...
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Transport properties of pure and doped Eu chalcogenides are reviewed to determine the mechanisms responsible for the anomalous behavior near Tc, the Curie temperature. It is found that, whereas the scattering theory of simple metals accounts for the behavior of materials containing impurities in excess of 2 × 1020 cm−3, several models for transport ha...
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The conductivity of EuO has been measured as a function of temperature from 30 to 300°K in magnetic fields up to 50 kG. The zero-field resistivity exhibits a sharp elbow at about 50°K, and increases as much as 108 between 50 and 70°K to a broad maximum between 75 and 80°K. In an applied magnetic field, the broad maximum is rapidly decreased and the elbow is s...
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The observation of zero-bias anomalies in tunneling has received much attention but their interpretation has suffered from a lack of definition of the character of the tunneling barrier. Junctions formed from a metal with Eu-chalcogenide ferromagnetic semiconductors offer a potential means of overcoming this difficulty. We have made rectifying junctions of EuS:Eu on In. The results indicate: 1) a ...
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Magnetic semiconductors are characterized by the presence of charge carriers and magnetic moments. The interaction between the charge carriers and the magnetic moments leads to a spin splitting of the energy bands, and to spin-disorder scattering of the charge carriers. The result is a strong influence of magnetic properties on the transport properties. The theory of these effects is discussed in ...
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A phenomenological model is presented to explain the anomalous temperature dependencies of the electrical resistivity and the Hall and Seebeck coefficients of indium-doped CdCr2Se4 with selenium deficiencies. The model postulates the existence of a hole band below localized donor levels, well above the intrinsic valence band. The assumed relative motions of the hole band and ...
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The high-field longitudinal magnetoresistance of the ferromagnetic (polycrystalline) p-type semiconductor AgxCd1−xCr2Se4 has been measured as a function of temperature and applied magnetic and electric fields. It is suggested that the observed “anomalies” may be related to the possible spin wave-carrier wave interactions in these mat...
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Several aspects of electronic transport in nonmagnetic and magnetic transition metal oxides are reviewed. These include high- and low-temperature measurements of conductivity, the Hall effect and the Seebeck effect, and their analysis in terms of the electronic energy structure. Particular emphasis is put on the temperature dependence of the Hall mobility, which gives essential information concern...
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The measured optical properties of the Eu chalcogenides are surveyed in an attempt to determine those aspects of the electronic structure of these materials that have been established. Optical absorption as well as optical and magneto-optical reflectivity data are discussed, along with the results of photoconductivity, photoluminescence and photoemission measurements and of magneto-optical measure...
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The reflectivity of the ferromagnetic semiconductors EuO, EuS and EuSe has been measured as a function of temperature and light polarization in an orienting magnetic field. In the energy range from just above the absorption edges to about 5.0 eV, there are two prominent features, E1 and E2, which change with the magnetic order, indicating exchange splittings of the 5d states....
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The 4T1 and 4T2 crystal-field transitions of Cr3+ have been observed in the absorption spectrum of CdIn2S4(Cr). From the similarity between the temperature dependence of the 4T2 band and the reported blue shift of the absorption edge of CdCr2S4 it is concluded that in CdCr...
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Measurements of the magneto-optical rotation in CdCr2Se4 at wavelengths between 0.9 and 1.3 µm are reported. In the paramagnetic state, the rotation passes a minimum with decreasing wavelength and changes sign at the absorption edge. The Verdet constant is proportional to the paramagnetic susceptibility (V = −18 deg/kOe-cm at 300°K and λ = 1.05 ...
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The optical absorption coefficient for magnetic semiconductors has been calculated for indirect transitions in which the intraband scattering arises from an s-d or s-f exchange interaction instead of the usual phonon mechanism. The temperature and magnetic field dependence of the resulting absorption coefficient are discussed.
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This paper summarizes the recent investigations of photoinduced effects in magnetic materials. To date it has been shown that the uniaxial anisotropy, strain, linear dichroism, coercive force and initial permeability can be modified by infrared radiation. The theory interpreting the coercive force and permeability experiments differs from the model used to describe the first three effects and is n...
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Aims & Scope

The IBM Journal of Research and Development is a peer-reviewed technical journal, published bimonthly, which features the work of authors in the science, technology and engineering of information systems.